1. Technical Field
The present disclosure relates to radar and communications applications and in particular to those including phased arrays of antennas.
2. Description of Related Art
A phased array is a group of antennas in which the relative phases of the respective signals feeding the antennas are varied in such a way that the effective radiation pattern of the array is reinforced in a desired direction concomitantly with pattern control in undesired directions. Phased arrays come in several basic forms but are typically characterized by: an ensemble of radiating elements (the ‘antennas’ referred to above), a means to illuminate the elements that operates reciprocally as a beamformer (also called a feed network or manifold), an amplification, phasing and control/logic layer, an RF signal, timing and control, a power distribution layer (or mainfold), and associated support structure. Phased array antennas are almost exclusively assembled as monolithic planar structures because of the need for contiguous conductors for two-way distribution of signals, control logic, and data across the full array area. These structures frequently take the form of multilayer printed circuit boards. The feed may either be via constant electrical path length conductors or via broadcast (e.g., space feed). Current phased arrays have several drawbacks. These include: high cost, difficulty of transporting large arrays (because large arrays must be handled as unitary entities—because of contiguous signal, control and/or power distribution manifolds), high repair costs (typically about five percent of modules may fail before modules must be replaced), and high phased array antenna areal density (mass per unit aperture area).
Extensive efforts are being undertaken to reduce array costs. Evolving technical solutions directly attach transmit/receive (T/R) modules (or T-only or R-only modules) to the array backplane, instead of individual “plug-in” units. Maximizing the cost benefits of commercial assembly (for planar circuit boards) has led to more complex multi-layer circuit boards being employed. When the requisite number of failures in an antenna has occurred and the modules need to be replaced, whole panels are replaced, by disassembling the antenna, with the attendant intra-antenna interconnect issues. The panels then are factory disassembled (costs are not yet sufficiently low to discard the panel) and hand reassembled.
Incorporation of fiber optics can reduce the weight associated with signal, data, control, and beamforming manifolds. However fiber optics cannot carry the power levels necessary to operate the array, thus maintaining the monolithic array backplane for power distribution. In the case of fiber optics the weight is decreased along with system maturity while cost is increased because of the more immature photonics technologies. The power manifold and its associated weight are unaffected. Routine fold/disassembly/deploy operations are not possible in current high frequency systems. Even with photonics, the array cannot be disassembled for shipping/transport then reassembled for operation unless a complete recalibration is performed each time. Therefore, the backplane is transported in one piece, which is problematic for highly mobile users who must then fall back on non-array antenna solutions.